app.py

import openpyxl as xl
from openpyxl.chart import BarChart, Reference

wb=xl.load_workbook('transactions.xlsx')
sheet=wb['Sheet1']
cell=sheet['a1']
cell=sheet.cell(1,1)
print(cell.value)
print(sheet.max_row)
for row in range(2, sheet.max_row + 1):
   cell = sheet.cell(row,3)
   print (cell.value)
   corrected_price = cell.value*0.9
   corrected_price_cell = sheet.cell(row,4)
   corrected_price_cell .value = corrected_price
   print(corrected_price_cell.value)

values=Reference(sheet,

   min_row=2,
   max_row=sheet.max_row,
   min_col=4,max_col=4
)

chart=BarChart()
chart.add_data(values)
sheet.add_chart(chart,'e2')

wb.save('transactions3.xlsx')